Method for producing lead oxide



April 5, 1% F. M. COPPERSMITH ETAL METHOD FOR PRODUCING LEAD OXIDE 2Sheets-Sheet 1 Original Filed Feb. 16, 1961 SETTLING CHAMBER TO STORAGEF. M. COPPERSMITH ETAL 3,244,563

METHOD April 5, 1356 FOR PRODUCING LEAD OXIDE 2 Sheets-Sheet z CriginalFiled Feb ahm 5 United States Patent Ofifice Patented Apr.v 5, 1966 4Claims. (Cl. 136-27) This application is a division of our copendingapplication, Serial No. 89,735, filled February 16, 1961.

This invention relates to an improved process and apparatus formanufacturing a new composition of finelydivided lead oxides and leadwhich is particularly suitable for manufacturing the plates used in leadstorage batteries, including those batteries known as the S.L.I. type(starting, lighting and ignition).

Lead oxide-lead mixtures used in the making of the plates for leadstorage batteries have been manufactured for many years by two differentprocesses. One such product has been made by an attrition procedure inwhich solid pieces or chunks or metallic lead are tumbled in a ball millor drum through which a stream or air flows. In the attrition process,lead oxide formed as a skin on the chunks of solid metal is knocked offby the tumbling action, together with small flakes of metallic lead, andthe product is removed from the ball mill or drum either by overflowingat the outlet, or by being carried away in the air stream.

The product of the attrition process is a mixture containing usuallyabout 15 to 30% by weight of thin metallic lead particles, with thebalance composed of even smaller particles of litharge (PbO) almostentirely in the tetragonal crystal form. One of the recognizeddisadvantages of this product for manufacturing the plates used in leadstorage batteries is that it is not feasible to produce a product inwhich the metallic lead content is substantially above about 30% byweight of the total product and yet provide a satisfactory battery leadoxidelead product. In products produced by the attrition processcontaining more than about 30% by weight of metallic lead, the metalliclead particles are of too large a particle size to properly hydroset inproducing lead storage battery plates by conventional practices.

The other general type of product used for making battery plates isproduced by the oxide pot or Barton pot operation, in which molten leadis fed into a pot and vigorously agitated by a stirrer while a stream ofair passes through the pot and carries off the desired product throughan uptake into a settling chamber. In this process, the pots areoperated at temperatures well above the melting point of lead (621 F.)and the particles of both lead oxides and metallic lead are more or lessround in shape, and not fiat. Here again, the product usually varies incomposition from around 15 to 30 or 35% metallic lead, with the balanceconsisting of a mixture of the two different crystal forms of litharge(PbO), tetragonal and orthorhombic. At contents of above about 35% byweight of metallic lead the product is unsatisfactory for themanufacture of battery plates by conventional procedures because it doesnot hydroset properly. By controlling the rate of air flow and theaverage temperature of the pot operation as described in Mayer PatentNo. 2,235,487, it has been possible heretofore to obtain a productreasonably uniform with respect to the percentage of metallic lead andthe relative proportions of tetragonal litharge and orthorhombiclitharge. The particles of free metallic lead in the Barton oxideproduct are not only different in shape, being more or less round inshape, but usually average somewhat smaller in size (about 15 to 20microns on the average) than the flat metallic lead particles in theball mill product.

Efforts have been made heretofore by grinding and other techniques tomake such products with particles of even smaller sizes, but they haveonly been successful in reducing the size of the lead oxide particles.The metallic lead particles are so malleable by their nature thatgrinding or the like merely changes their shape without substantiallyreducing their diameter on the average. As a consequence, the bestBarton oxide products, even after milling, have contained oxideparticles averaging 2 to 4 microns in diameter, while the metallic leadparticles averaged 15 to 20 microns in diameter. The ball mill productscontain even larger particles of metallic lead.

One object of this invention is to provide a novel process formanufacturing a new lead oxide-lead product which has many advantagesover either of the foregoing when used in making plates for lead storagebatteries. Another object of this invention is to provide a novelprocess for manufacturing a Barton pot type of oxide product in whichthe particles of metallic lead are not in the usual shape, but are fiatplatelets of only about 1 to 1.5 microns in thickness rather than moreor less jagged irregular particles as have been obtained by prior artBarton oxide processes.

A further object is to provide a process for producing an improved leadoxide product which contains a substantially larger number of particlesper unit of weight than the prior products produced by the Barton oxideprocess.

Still another object of this invention is a provision of improvements inthe Barton oxide apparatus and process which make it possible to producethe foregoing new product.

Certain more or less empirical tests have been employed for judging thequality of a lead oxide-lead product used for making lead storagebattery plates. Two of the most frequently use-d tests for this purposeare the apparent density test and the acid absorption test. The apparentdensity is determined by filling a one-inch cubical measuring cup withthe product under a specified procedure and weighing the contents.Apparent densities of 22 to 28 or 29 grams per cubic inch have beenconsidered acceptable in the past for Barton oxide products. Bartonoxide products prepared according to this invention can be readily madehaving an apparent density in the order of 18 to 22 grams per cubicinch.

The acid absorption of the material is determined by a standard butempirical procedure in which a weighed amount of the product is treatedwith sulphuric acid, and the amount of the acid absorbed in a certaintime is de termined. Acid absorptions of to (in terms of milligrams of H80 absorbed by one gram of oxide product) have been considered veryacceptable in the past for Barton oxide products, whereas the productsof this invention can be readily made with acid absorptions above about180, preferably from about 200 to 220.

In the manufacture of plates for lead storage batteries, the oxide-leadproduct is first made into a paste with the addition of water andusually as an additional liquid, sulphuric acid. This paste is thenpressed onto an open work cast grid and dried to form the plate in aprocess known as hydrosetting. During the drying of the paste, thefinely-divided metallic lead should be largely or completely convertedto lead oxide with spontaneous generation of heat. It is generallyrecognized that it is desirable, particularly in making the positiveplates, to have no substantial residue of metallic lead in the driedpaste upon completion of the drying operation. In using the product ofthis invention to make battery plates, the paste can be made with amaterial that is relatively high in free metallic lead without leavingany undesired residue of unoxidized metal upon drying. Additionally, thehigher concentration of metallic lead produces a greater quantity ofexothermic heat, thereby accelerating the hydrosetting operation. Also,we have found that battery plates can be made from our new oxide productusing about 10 to 20% less paste or weight of solid product per platethan heretofore considered necessary and still produce a storage batterythat meets all of the required discharge, voltage, life and other testsestablished as standard for storage batteries by the Society ofAutomotive Engineers.

The process and apparatus of the invention will be better understood byreferring to one suitable form of apparatus shown in the accompanyingdrawings in which:

FIG. 1 is a side elevational view partly in section of a Barton pot,uptake, settling chamber, and associated parts modified so as to besuitable for making the new product of this invention.

FIG. 2 is a plan view of the modified Barton pot, an associated meltingpot, the uptake and part of the settling chamber as shown in FIG. 1.

FIG. 3 is a plan view of a modified Barton pot shown on a larger scalethan in FIG. 1.

FIG. 4 is a vertical sectional view of this improved Barton pot takengenerally on the line 44 of FIG. 3.

FIG. 5 is a vertical sectional view of the pot taken on the line 55 ofFIG. 3.

Referring to the drawings, and particularly FIGS. 1 and 2, the apparatusof this invention is similar to that shown in Mayer Patent 2,235,487 buthas been modified in various respects which we have found desirable forproducing our new oxide material. For example, the apparatus includesbasically a Barton pot mounted in suitable foundations 11 andprovidedwith a rotary stirrer or agitator 12 carried on a vertical shaft 13.Lead is melted in a suitable melting pot 14 and a continuous stream ofthe molten lead is fed through a suitable feeding device 15 from themelting pot 14 into the Barton pot 10. The rate of flow of the moltenlead may be controlled by the type of apparatus shown in said Mayerpatent or by any other suitable valve arrangement capable of providing acontinuous flow of molten lead at a controlled variable rate. Air flowsinto the Barton pot through an intake 16 and the product, consisting ofa finely-divided mixture of lead oxides and metallic lead, is carriedoff through an uptake 17 to a settling chamber 18, where it falls to thebottom of the chamber and is removed to storage or further treatment bya screw conveyor 19 or other suitable means. Affixed to the uptake 17 isa vibrator 17a so as to prevent build-up of product in the uptake. Theconstant action of the vibrator provides steady return of a portion ofthe product which collects on the walls of the uptake to the Barton potto provide a more constant supply of dross in the Barton pot. A streamof air through the Barton pot 10, the uptake 17 and settling chamber 18is created by a suction fan 20 and the rate of flow of air is controlledby a suitable damper or valve 21.. The rate of air flow can be measuredat the intake 16 by means of the usual Pitot tube 22 and either recordedor used to vary the position of the damper 21 to maintain a constantdraft by suitable mechanism (not shown).

A fixed radical baflie 23 is preferably positioned within the pot 10 soas to be on the side of the uptake farthest from the molten lead inletwhen the stirrer is rotated in the direction of the arrows indicated inFIGS. 2 and 3. A suitable pyrometer or other temperature measuringdevice 24 may be located adjacent the baffle 23 in a position to beprotected by it, and may be connected to a suitable temperatureindicating or recording device (not shown).

Referring now more particularly to FIGS. 3, 4 and 5, the Barton potproper can be made of the usual base sec tion 25 and cover section 26which are provided with suitable flanges 27, so that they can be boltedor otherwise attached together. The cover section 26 is provided onopposite sides with an outlet opening 28 to which the uptake 17 isattached and with an opening 29 through which the air inlet pipe 16extends. The air inlet pipe differs from the usual Barton potinstallation in that it extends down into the lower portion of the potand introduces the air within a few inches above the top of the stirrer.This inlet pipe may be perforated or cut away at the bottom as at 30 onthe side away from the motion of the stirrer. The cover section 26 ofthe pot is also provided with a spout or lip 31 through which the moltenlead is introduced, this molten lead inlet being located about half waybetween the air inlet and the uptake. The radial bafiie 23 is preferablypositioned differently and made larger than usual so that it extendsabout half way into the center of the pot and also extends from the topdown to a point approximately as far as the air inlet 16. The outletopening 28 and the uptake 17 attached to it are preferably made muchlarger than usual in a cross section, and the uptake 17 is made muchlonger than is customary in Barton pot operations. We have found, forexample, that a cross-sectional area of 800 square inches compared tothe normal 400 square inches, combined with an uptake length ofapproximately 20 feet compared with the usual 6 to 8 feet, .ispreferable for operation in accordance with our invention. Such aconstruction provides better classification of particle sizes of theproduct. The less desirable larger sized particles are more likely to bereturned to the Barton pot where they undergo further oxidation andgrinding off of the oxide coating by the dross in the bottom of the potto reduce particle size to that desired in accordance with theinvention.

Since the air inlet pipe 16 extends down into the lower portion of theBarton pot it provides for greater cooling of the dross being agitatedin the bottom of the pot and better utilization and circulation of airthrough the apparatus and better control of the temperature.

The larger size of'the radial baffle 23 and its position before theuptake reduces the likelihood of large sized particles of material beingswept up into the uptake. Therefore, only the smaller sized particlesare likely to be removed from the Barton pot. This construction alsohelps to retain sufficient dross inthe Barton pot to dis perse themolten lead as it enters the pot into finely divided droplets beforethey freeze. The finely-divided lead particles in the frozen state willoxidize at a slower more uniform rate and provide a more desirable sizedparticle in the final product.

In the operation of this equipment the pot is started in the usualmanner by heating it and running in a charge of molten lead. Theheat-under the pot is then turned off, the agitator or stirrer 12 isstarted rota-ting and the suction fan 20 is turned on. Thereafter it isusually not necessary to supply any heat to the system except for thatprovided by the exothermic reaction and the molten lead. Each time onearm of the stirrer 12 comes around, it throws the load of the potviolently against the baffle 23 which causes the material in the pot tobe broken up into very fine particles. The flow of air from the inlet 16through the pot and out the uptake 17 serves three dilferent functions.It supplies the oxygen needed to oxidize metallic lead to lead oxide; itacts as a conveyor to carry the product out of the pot through theuptake 17 to the settling chamber; and it exerts a substantial coolingeffect on the pot and its contents. The flow of air is usually ad justedby trial and error to produce a product of the desired percentage offree metallic lead, and thereafter it is varied only slightly during thecourse of operation.

Although the pot operation is started with molten lead, the mass ofmaterial in the pot is soon converted into a dross, which is a mixtureof solid granular lead oxides and lead (both molten and solid) and whichis violently agitated and periodically thrown up against the baffle bythe stirrer. We have found that by using a suitable baffie just ahead ofthe uptake, introducing the air into the lowest portion of the pot, andusing a greatly enlarged and lengthened uptake equipped with a vibrator,the operation of the pot can be controlled so as to produce a productwith both metallic lead and lead oxide of very fine particle size and,at the same time, the operating temperature of the pet can be maintainedlow enough so that no more than 15% of the lead oxides in the productare in the form of the orthorhombic crystal modification. In the usualprior art Barton pot operation, the rotation of the stirrer is about 150r.p.m. By increasing this speed of rotation, for example, to about 300rpm. we

have found that it is easier to produce the desired product of thisinvention at highly efiicient rates.

An important feature of the process of the present invention is tomaintain a leady oxide dross in the Barton pot during the process. drossin the Barton pot by means of the particle size classification systemprovided by the operation of the uptake 17, whereby larger, over-sizedparticles are returned to the pot for further oxidation and sizereduction and the desirable size particles are recovered in the settlingchamber 18. When the molten lead feed is directed into the pot it isimmediately finely dispersed in the leady oxide dross before it has hadan opportunity to freeze. This assists in markedly reducing the particlesizes of the lead oxide particles, and also of the unoxid zed metalliclead. By continuing a low rate of feeding the molten lead and increasingthe rate of air flow, it is possible to operate the pot at temperaturesbelow the melting point of lead (621 F.) ranging down, in some cases, toas low as 300 F. Preferred temperatures are between about 400 and 500 F.The discovery that the lead in the pot could be oxidized at highlyefficient commercial rates wherein the pot content has an averagetemperature below the melting point of lead was surprising. We havediscovered that maintaining the temperature below the melting point oflead is essential in producing a lead oxide-lead composition wherein theparticles of both lead oxide and metallic lead in the final product areof very fine particle size and high metallic lead content, accompaniedby a very high acid absorption value, low apparent density, and otherproperties which make the composition of the invention greatly superiorto the lead-lead oxide products heretofore available for making leadstorage battery plates. Maintenance of the contents of the Barton pot atan average temperature of below the melting point of lead constitutes animportant feature of the present invention.

The process of the present invention permits economical production of asuperior lead-lead oxide product. In accordance with the invention athigh rates of production it is possible to feed the molten lead into theapparatus at rates of 1000 to 1500 pounds per hour in apparatus of thesize described hereinabove.

It is possible to maintain the a In order more clearly to disclose thenature of the present invention, specific illustrative examples will beset forth. It should be understood, however, that this is done solely byway of example and is intended neither to delineate the scope of theinvention nor limit the ambit of the appended claims. Parts areexpressed in terms of parts by weight.

Example 1 Employing the apparatus and process described hereinabove inconjunction with the drawings and operating the stirrer at a rate of 300rpm, maintaining the contents of the Barton pot at a temperature of420440 F, introducing the molten lead into the pot at a rate of 11001150 pounds per hour, introducing air into the inlet tube at a pressureof 0.5 inch of water as measured by a Pitot tube with the air inlethaving a diameter of 10 inches, a product was obtained containing 43.5%metallic lead, 10-12% orthorhombic lead oxide and the remaindertetragonal lead oxide. The product had an apparent density of 20.8 andan acid absorption value of 201. The metallic lead particles had anaverage thickness of l1.5 microns. This lead-lead oxide productpossessed excellent properties for producing lead storage batteries.

It would not have been possible to produce compositions having the highpercentage of metallic lead and the thinness of less than 1.5 microns ofthe metallic lead particles obtained in the foregoing example byemploying the prior art Barton oxide process or the ball mill process.

Example 2 Employing the apparatus and process described hereinabove inconjunction with the drawings and operating the stirrer at a rate of 300r.p.m.., maintaining the contents of the Barton pot at a temperature ofabout 480 F., introducing the molten lead into the pot at a rate ofabout 1173 pounds per hour, introducing air into the inlet tube at apressure of 0.6 inch of water as measured by a Pitot tube with the airinlet having a diameter of 10 inches, a product was obtained containing48.5% metallic lead, l0l2% orthohombic lead oxide and the remaindertetragonal lead oxide. The roduct had an apparent density of 22.1 and anacid absorption value of 205. The metallic lead particles had an averagethickness of l-l.5 microns. This lead-lead oxide product possessedexcellent properties for producing lead storage batteries.

The novel lead-lead oxide products produced in accordance with theprocess of the invention have unique properties which are greatlysuperior to the products heretofore available for making lead storagebattery plates. The products of the invention have an acid absorptionvalue of at least about 180, apparent densities of about l822, a contentof metallic lead of at least about 38% by weight, up to about 60%, andpreferably between about 40 and 50% by weight of product, an averagethickness of metallic lead particles of between about 1 and 1.5 microns,anorthorhombic lead oxide content of between about 5 and lead oxideparticles of average-particle size of less than one micron, with thenumber of particles per cc. of product being between about 1.8 and22x10, when measured by microscopical methods for particle sizedistribution of particulate substances of subsieve sizes according toA.S.T.M. Method E51T, issued 1933 and revised in 1948 and 1951.

The products of the invention also have a cube weight of 565-58 whenconverted to a paste prepared by mixing one pound of product with cc. of1.4 specific gravity sulphuric acid and sufficient water to give aconsistency value of 10 when measured in accordance with test procedureswell known to the art.

The unique nature of the properties of the products produced inaccordance with the process of the present invention is brought out by acomparison with the values obtained for typical products made by priorart Barton a oxide procedures and by the ball mill process. shown inTable 1 below:

This is TABLE I Products of the process Typical Barton oxide TypicalBall mill Property of the present invention products of the prior artproducts the prior Acid absorption Above about 180 250-275. Apparentdensity 18-22 so 18.5-20.5. Average particle size of lead Less than 1micron 2.7-3.0 microns Less than 1 micron.

oxide particles. P(ii(l8lltdby weight of metal- At least about 33%15-35% 15-35%.

to lea Average thickness of metal- 1-1.5 microns Jagged particles ofvary- 1-1.5 microns.

lic lead particles. ing thickness. Percent by weight of orthor 5-157515% Less than 1%.

homhie lead oxide. Cube weight of paste 55.5-58 65-66 61.5-63.5. Numberof particles per ec.. 1.8 to 2.2 l0 0.25 to 040x10 1.2 to 115x10".

need be employed to produce a battery plate and yet I meet the standardS.A.E. tests for storage battery plates. Expressed in another way, thelead-lead oxide products of the invention provide a 10 to increase incapacity per unit amount of lead oxide product over the comparablebattery lead oxide products of the prior art. This increase in capacityis achieved without loss in other properties which are necessary incommercial lead storage battery plates. This saving is even moresignificant when one considers that approximately 200,000 tons of leadoxide product are employed annually in the production of lead storagebattery plates.

Another unique characteristic of the products produced in accordancewith the invention is that they absorb more water and sulphuric acidthan do the conventional prior art lead oxide products and still producea paste satisfactory tor the production of battery plates. This, inpart, explains why the battery manufacturer may employ less lead oxideproduct in producing the pastes which are applied to the grids inproducing battery plates.

Another important advantage of the products produced in accordance withthe invention, which we believe results from their higher metallic leadcontent, is that they produce a greater amount of heat during thehydrosetting process and thereby provide greater binding power of thepaste to the grid andexpansion of, the paste during drying. This in turnprovides a more porous coating, having more surface area, and this inturn may account in part for the higher ca acity or etliciency inbattery plates produced from the lead-lead oxide products in accordancewith the present invention.

Some of the advantages of the lead-lead oxide products produced inaccordance with the present invention over a standard. commercialproduct of the prior art produced by the Barton oxide process will bedescribed below, employing the product of the invention produced inaccordance with Example 1 hereinabove.

In conducting the test a determination is first made of the amount of1.4 specific gravity sulphuric acid and water which both lead oxideproducts will absorb to produce a paste of a consistency value of 10units when determined by the standard procedure employed in the art. InTable II below are compared the amounts employed and the resulting cubeweights.

Positive paste pounds of the product of Example 1, 92 cc. of water perpound of product of Example 1, 40 cc. of 1.4 specific gravity sulphuricacid per pound of product of Example 1, were blended to produce a pastehaving a consistency of 9 units and a cube weight of 57.5.

Negative paste 49 pounds of the product of Example 1, l pound-ofstandard negative battery plate expander, cc. of water per pound ofproduct of Example 1, 29 cc, of 1.4 specific gravity sulphuric acid perpound of product of Example 1, were blended to provide a paste having aconsistency of 10 units and a cube weight of 65.

From the positive and negative plate pastes described above, batteryplates were produced in accordance with standard commercial productionpractices and cells prodnced each containing 7 positive and 8 negativeplates.

Listed below, in Table III is the amount of dry weight of lead oxideproduct applied as a coating to each plate grid. In cells 11 and 12there was employed a paste produced from the same commercially availableprior art Barton oxide product employed in Table I.

TABLE III plate plate Cells 1 and 2 Positives..- 3. 33 Negatives... 3.18 Cells 3 and 4.. 3. 53 .d 3. 18 Cells 5 and 6-. 3.45 do.. 3.26 Cells 7and 8.. 3. 53 d0 3. 38 Cells 9 and 10. 3.33 ..do. 3.83 Cells 11 and 1 3.85 Control.. 8.

The cells were then subjected to efiiciency tests to determine theetliciency of the cells at a discharge rate of 5 amps. over a 20-hourperiod and to the standard cold test at 0 F. The results in Table IVbelow tabulate the average obtained for each set of two cells at aS-ampere discharge rate in terms of ampere hours at the 20-hour rate.The cold test measures the number of minutes for the cell to dischargeat a. discharge rate of 300,amps. at 0 F. i

In Table V below is computed the efficiency of the plate in terms ofampere hours per ounce of dry weight of unforrned positive plate activematerial per cell at the 20-hour rate.

TABLE V ZO-hour eficiency test Ampere N0. of Av. Total Ampere Hrs. perPos. Weight, Weight, rs. oz.[d ry Plates oz. oz. Obtained positive platematerial Cells 1 and 2- 7 3. 33 23. 31 98.8 4. 24 Cells 3 and 4.-.. 7 3.53 24. 71 103. 8 4. 20 Cells and 6.. 7 3. 45 24.15 102. 5 4. 24 Cells 7and 8. 7 3. 53 24. 71 104. 6 4. 23 Cells 9 and 10.. 7 3. 33 23. 31 99. 74. 28 Cells 11 and 12 (Control) 7 3. 85 27. 02 98. 3 3. 64

As shown from the foregoing Table V, when the average of the resultsobtained from cells 1 through are compared with the control cells 11 and12, the product of Example 1 is approximately 16.5% greater in capacitythan the commercially available prior art Barton oxide composition Whenthe battery plates prepared from the lead oxide product of Example 1were subjected to the S.A.E. life test, cold test and other standardtests employed in evaluating lead storage batteries, they passed all ofsuch tests.

The terms and expressions which we have employed are used as terms ofdescription and not of limitation, and we have no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but recognize thatvarious modifications are possible Within the scope of the inventionclaimed.

What is claimed is:

1. In a process of operating a Barton type of oxide pot to make abattery oxide product, the steps of introducing a stream of air into thelower portion of the pot just above the stirrer therein, feeding moltenlead into the pot in a continuous stream in a sufliciently small amountto maintain the contents of the pot at a temperature below the meltingpoint of lead, vigorously agitating the pot contents by periodicallydashing them against a large fixed baffle, carrying oif the product fromthe pot through an elongated uptake and during the operation of said potcontinuously maintaining a dross of particles of metallic lead and leadoxides in said pot in sufficient amount to provide a medium fordispersing the molten lead as it is introduced.

2. A process of opera-ting a Barton type of oxide pot as defined byclaim 1, wherein the contents of the pot are maintained at a temperatureof between about 300 and 621 F.

3. A process of operating a Barton type of oxide pot as defined by claim1, wherein the contents of the pot are maintained at a temperature ofbetween about 400 and 500 F.

4. A process as defined by claim 1, wherein the dross is maintained inthe pot by continuously returning to the pot a portion of the largerheavier particles which are carried into the elongated uptake.

References Cited by the Examiner UNITED STATES PATENTS 846,444 3/1907Bailey 23146 1,770,777 7/1930 Haynes 23279 1,913,391 6/1933 Hutchinson23146 2,235,487 3/1941 Mayer 23146 2,380,096 7/1945 Doan et a1. 136-26.12,383,220 8/1945 Seabury et a1. 23146 ALLEN B. CURTIS, Primary Examiner.

JOSEPH REBOLD, JOHN R. SPECK, JOHN H. MACK,

Examiners.

1. IN A PROCESS OF OPERATING A BARTON TYPE OF OXIDE POT TO MAKE ABATTERY OXIDE PRODUCT, THE STEPS OF INTRODUCING A STREAM OF AIR INTO THELOWER PORTION OF THE POT JUST ABOVE THE STIRRER THEREIN, FEEDING MOLTENLEAD INTO THE POT IN A CONTINUOUS STREAM IN A SUFFICIENTLY SMALL OFMETALLIC LEAD AND LEAD OXIDES IN SAID POT IN SUFFICIENT TURE BELOW THEMELTING POINT OF LEAD, VIGOROUSLY AGITATING THE POT CONTENTS BYPERIODICALLY DASHING THEM AGAINST A LARGE FIXED BAFFLE, CARRYING OFF THEPRODUCT FROM THE POT THROUGH AN ELONGATED UPTAKE AND DURING THEOPERATION OF SAID POT CONTINUOUSLY MAINTAINING A DROSS OF PARTICLES OFMETALLIC LEAD AND LEAD OXIDES IN SAID POT IN SUFFICIENT AMOUNT TOPROVIDE A MEDIUM FOR DISPERSING THE MOLTEN LEAD AS IT IS INTRODUCED.